The role of complexions in metallic nano-grain stability and deformation

Nanocrystalline metals have excellent strength due to the high density of grain boundaries inside. However, these same boundaries lead to limited thermal stability and a tendency to fail in a brittle manner, issues which limit the practical usage of these materials. Most strategies for stabilization of nano-grains against coarsening rely on the idea of using segregating dopants to lower excess boundary energy. The theory of interface complexions is a useful tool for describing the thermodynamics behind segregation as well as identifying distinct segregation patterns. Some of these same complexions can also dramatically alter mechanical behavior. Unlike past strategies, which always result in a trade-off between strength and ductility, the addition of complexions can potentially increase ductility while retaining or even increasing strength. In this paper, we discuss how complexions offer a unique opportunity to address these limitations simultaneously. In addition to reviewing the current-state-of-the-art, important areas where innovation is needed are also identified. 2016 Elsevier Ltd. All rights reserved.